Computational Modelling of Polyoxometalates: Progress on Accurate NMR Characterization and Reactivity

Identificador:  TDX:2552

Handle: https://hdl.handle.net/20.500.11797/TDX2552

Autors:  Pascual Borràs, Magdalena

Resum:
This thesis can be divided in two different parts: i) NMR and ii) Reactivity. The common factor of both sections is Polyoxometalates (POMs). POMs are polymetallic molecular anions formed upon aggregation of octahedral MO6 blocks made of early transition metals (TMs), in their higher oxidation states, and oxygen, that are connected commonly by vertices and edges. The first part is related to the characterization of POMs. In particular, it is based on the calculation of nuclear magnetic resonance (NMR) spectroscopy parameters. First, we focused on 17O nuclei. We have established a DFT-based strategy to accurately compute and rationalize 17O NMR chemical shifts of polyoxoanions. We show that calculations performed with GGA-type PBE functional, including spin-orbit and scaling corrections, provide a mean absolute error value (MAE) <30 ppm, a small value considering the large range of δ(17O) chemical shifts in POMs. A study for the best DFT strategy for the determination of 31P NMR chemical shifts in POMs is also reported. We have described the first thallium containing polyoxometalate, which was synthetized and structurally determined. A detailed study of 203/205Tl NMR has been performed in order to reproduce the experimental values. The δ(205Tl) are really well reproduced with DFT methodology. However, in the spin-spin coupling, there are large differences between calculated and experimental 2J(205Tl-203Tl).